Light emitting diodes (LEDs) have been widely used in proximity sensing. In particular, LEDs have been paired with photodiodes in optical sensing systems. For example, an optical sensing system may drive an LED to emit light in certain wavelength range. This emitted light is received by a photodiode after going through a medium or being reflected by a surface. The photodiode converts the received radiant energy to electrical current which is further processed for detecting, for example, the existence of a moving object.
An optical sensing system may include multiple pairs of LEDs and photodiodes to form a sensing network for detecting an object's position, moving speed, and moving direction. For example, the sensing network may be installed along a track through which the object moves. Detection resolution and accuracy may require the multiple pairs of LEDs and photodiodes to be placed close to each other. Unfortunately, a photodiode may capture radiant power from nearby LEDs (interfering radiant power) in addition to the LED that the photodiode is paired with, causing false detection. For example, the interfering radiant power may falsely trigger the detection threshold of the photodiode and decreases the system sensing resolution. Such false detection may not be tolerated in high-resolution optical sensing systems. Accordingly, improvements in this area are desired.